As a mechanism applied to an internal combustion engine for a vehicle or the like, a variable valve timing mechanism is known that makes valve timing of an engine valve variable. As a kind of variable valve timing mechanism, a hydraulic variable valve timing mechanism operating by hydraulic pressure is in practical use.
The hydraulic variable valve timing mechanism is operated such that hydraulic pressure supplied from a hydraulic pump driven by rotation of the engine is adjusted by an oil control valve. For this reason, at engine start when an oil pump begins to operate, the hydraulic variable valve timing mechanism may not receive hydraulic pressure sufficient to hold the valve timing. For this reason, in a large number of hydraulic variable valve timing mechanisms, lock mechanisms are installed that mechanically lock valve timings without the use of hydraulic pressure.
In a variable valve timing mechanism for intake valves, in general, locking of valve timing by a lock mechanism is performed at a most retarded position. On the other hand, in recent years, a variable valve timing mechanism that realizes an Atkinson cycle by considerably retarding the valve timing of an intake valve and late-closing intake valves has also been proposed. In the variable valve timing mechanism in which a variable range of valve timing is widened on the retarded side, a sufficient compression ratio cannot be obtained at the most retarded position, and an internal combustion engine cannot exhibit good startability. In such a variable valve timing mechanism, an intermediate lock mechanism that mechanically locks valve timing at an intermediate lock position between the most retarded position and the most advanced position is installed to set the valve timing at engine start to the intermediate lock position.
On the other hand, in recent years, a vehicle that executes idling stop control has been in practical use to automatically stop an internal combustion engine during vehicle stoppages such as waits at stoplights. In a hybrid vehicle, in an operation region in which the fuel efficiency of an internal combustion engine is low, the internal combustion engine is stopped so that driving is performed by a motor. For this reason, the internal combustion engine mounted on the vehicle is intermittently stopped while the vehicle is moving.
Conventionally, Patent Document 1 discloses that, in a hybrid vehicle including a variable valve timing mechanism, valve timing is set at the most retarded position when an internal combustion engine is intermittently stopped. Patent Document 2 discloses that, in an internal combustion engine including a variable valve timing mechanism with an intermediate lock mechanism, the valve timing is retarded from an intermediate lock position at an intermittent stop, and the valve timing is set at the intermediate lock position when stopping the engine normally by turning off the ignition switch.